Sound recording and reproducing system



June 1939- o. M. DUNNING 2,153,671

SOUND RECORDING AND REPRODUCING SYSTEM Filed Feb. 20 19 57 2 Sheets-Sheet l INVE-NVTOR Orville M. Dunning BY m2; 8 A ORNEY June 27, 193.9. o. M. DUNNING SOUND RECORDING AND REPRQDUCING SYSTEM 2 Sheets-Sheet 2 Filed Feb. 20, 1937 i ENVENTOR OI'VI/l MDunnmg BY f ORNEY ily recorded and reproduced with a minimum of v mutual arrangements of-controlling means for a v Patented June 27, 1939 UNITED STATES PATENT OFFICE 2.103.011 sonnn nnooanma am) nnmonuomo svsrau Orville M. Dunning, Glen itidge, N. J.. assignor to Thomas A. Edison, Incorporated, West Orange, N. 1.. a corporation of New Jersey v Application February 20, 1931, Serial No. 126,803

recordation and later reproduction of dictation,

conferences or other speech-it is recognized as often desirable during recordation to reduce automatically volume contrasts which may actually exist in the sound as received by the microphone or the like, sovthat the recording means records upon the record sounds of very much more nearly uniform amplitude. This of course is principally because the volume range which can be satisfactorily recorded is usually rather limited, whereas the volumerange oi the sound to be recorded may be very wide-as when one person first speaks at small distance from a microphone, and then he or another speaks at many times that distance. Volume contrast-reducing or range-compressing means are therefore frequently employed in systems of the type described.

It is true, however, that such means are necessarily at least somewhat distorting in their effect upon the sound.. I find that if effective such means are permitted to remain active during the functioning of the system for reproduction of sound as well as for the prior recordation of that sound, markedly unpleasant and highly inaccurate effects may be pr'oducedin other words, the distortions which such means functioning during reproduction does not at all aid in meeting the initial requirement for their use in the system-the minimization of volume contrasts in the recording proper.

It is an object of my invention to provide a sound recording and reproducing system by which sounds of wide volume range may be satisfactor- .distortion.

It is another object to provide a recording and reproducing system wherein volume contrasts are reduced only to a useful and not to a useless deree.

It is another object to provide a recording and reproducing system with an advantageous organization of portions and connecting means therefor, for fulfilling the broader objects of the invention.

It is another object to provide advantageous sound recording and reproducing system. It is v cutting upon wax records.

entail are squared. And it is to be observed that their.

8 Claims. (Cl. "ll-100.4)

another object to provide a novel arrangement of recordation-reproduction converting means in a system for performing both those functions.

Still another object is to provide useful additional control means operating concomitantly with such converting means. Still another-object is to provide an improved volume range-compressing or contrast-reducing v means, and control device therefor, for a sound recording system. Other and allied objects will more fully appear from the following description and'the appended claims. In the description reference is had to the accompanying drawings, of which:

Figure 1 is a partly elevational and partly schematic view of a sound recording and reproducing system according to my invention, the apparatus beingadjusted for recordation;

Figure 2 is a view of a portion of the apparatus of Figure l, re-adjusted for reproduction; and

Figure 3 ,is a view of another portion of the apparatus of Figure 1, illustrating optional modifications thereof.

Reference being had to Figure 1, there will be seen a recording and reproducing phonograph designated generally as l-purely by way of-example, of the type arranged for reproduction by The phonograph I may include for example the base 2, the righthand end standard 3, the carriage rods la and 4b, and a carriage 5 slidable along those rods. Underneath the path of the carriage is seen a mandrel 6, journalled for example at the far (left-hand) end of the phonograph, and carrying a cy1indricall3 record I. It will be understood that in actual usethe mandrel and record will be rotated, and the carriage meanwhile propelled slowly along the carriage rods, by means not herein necessary to show. On the carriage over the record may be carried-a recorder- I4 and reproducer" i3, in any desired arrangement relative to each other and to former only appears in Figure 1), which may be the carriage. The recorder and reproducer may have respective styli l2 and II (of which the I by means of a control lever ,8. "This lever may,

extend upwardly from a suitable top aperture (not shown) in the carriagei-a-iid may move the styll (and simultaneously perform any otheri'de: sired operations immediately upon the recorder and reproducer) through mechanism in the car-I riage not herein necessary to show. It may, however, be stated that the lever 8 is conveniently splined to the carriage rod to through the engagement of a key (not shown) on the lever with a key-way 4a in the rod, so that as the lever moved forwardly or rearwardiy the rod la will be rotated.

shows the lever B in Figure 1 shows the lever 8 in its most forward position,the rod 4a in its most counter-clockwise adjustment (as viewed from the right-hand phonograph end), and the recording stylus l2 engaging the record surface. Figure 2 solidly its most rearward position, the rod la in its most clockwise adjustment, and the reproducing stylus H engaging the record surface. Dottedly Figure 2 shows the lever 8 in a mid or neutral position, it being understood that with this lever position both styli may be out of engagement with the record surface. The recorder and rcproducer, and in particular their stylus means l2 and i i, will be understood to comprise record-cooperating translating means movable selectively by lever 8 into recording and reproducing relationships to the record.

The apparatus so far described with relation to the figures may be considered, for purposes of the present invention, as itself known; and in the same category may be placed a system of protective cams 9 and iii-these or equivalent means being frequently employed to prevent the removal of a record 7 from the mandrel 6 while either stylus is in engagement with the record surface. The earn 9 may be secured on the rod to, and may have the extending portion 9a disposed in the path of record removal when the lever B is adjusted (see Figure 2) for reproduction and the rod to is thus extreme clockwise. When the lever B is adjusted to neutral (dottedly shown in Figure 2) the cam 53 will occupy an intermediate position, dottedly shown, wherein its portion so, no longer prevents record removal. As the lever 8 is adjusted for reproduction, however, the surface 9b of the cam Q impinges on the surface 80b of the cam it, which latter is pivoted below and slightly to the rear of the cam 9, and forces a clockwise rotation of the cam Hi to bring its extending portion illa into the path of record removal.

The phonograph of Figure 1 is shown arranged to function for recordation with the microphone i as a pick-up device, and the amplifier 20 as a means of amplifying the output of the microphone for application to the recorder hi; further, it is shown arranged to function for reproduction with the loudspeaker i5, and the same amplifier 20 as a means of amplifying the output of the reproducer it for application to the loudspeaker. For recordation it is necesasry to connect the microphone i5 to the amplifier input terminals ii, and to connect the amplifier output terminals IE to the recorder is, for reproduction it is neccssary to connect the reproducer l3 to the amplifier input terminals ii, and to connect the amplifier output terminals 58 to the loudspeaker it. The apparatus for switching or changing of these connections as required is simplified by the grounding-i. e., the connection to a common potential-of one electrical terminal each of the recorder Hi, the reproducer i3, the microphone l5 and the loudspeaker l6, and of one of the amplifier input terminals l1 and of one of the amplifier output terminals l8; such terminal grounding has accordingly been shown in Figure 1, and the remaining terminal in each case may conveniently be designated as the live terminal.-

I make the connection switching automatically responsive to stylus manipulation by lever 8; more specifically, to rotation of the carriage rod 4a; and still more specifically, to movement of the protective cam II). To this end I may secure to the standard 3 a compound or multi-contact switch 22, having a member 22a of insulating material disposed to be impinged on and moved by a surface We of the cam l0, for example only when the lever 8 is moved into recording position. The switch 22 may include pole members 21 and 28; contact members 25 and 24 respectively adapted to be contacted by those pole members when the lever 8 is in recording position (Figure 1); and contact members 23 and 26 respectively adapted to be contacted by those pole members when the lever B is not in recording (a. g., is in reproducing or neutral) position (Figure 2). All these members may be in the form of leaf springs clamped in the conventional insulating stack 22b, which may in turn be secured to the standard 3 by bracket 220; the insulating member 22a above mentioned may be secured against the pole member 21?; and the pole members may be tied together for movement in unison by insulating tie means 2241. The live terminals of recorder it and reproducer it may be connected by leads 35 and 33 respectively to contact members 26 and 23; the live terminals of microphone i5 and. loudspeaker it may be connected by leads 35 and 36 respectively to contact mbembers 25 and 26; and the live one of the input terminals I1 and the live one of the output terminals It may be connected by leads 3? and 33 respectively to pole members 217 and 28. It will be seen that the switch structure and connections described in this paragraph meet the requirements set forth in the preceding paragraph.

While in the practise of my invention the volume contrast-reducing or range-compressing means are not necessarily limited to association with an electrical amplifier, such an association is a particularly convenient arrangement and has been illustrated herein. Accordingly the amplifier is provided with an automatic volume control" circuit, which functions to regulate the amplifier gain approximately in inverse accordance with the volume applied to the amplifier input. In Figure 1, 2c represents a typical amplifier provided with a typical control circuit of the type just mentioned; it may now be described more in detail, it being understood, however, that the amplifier and volume control description is not to be taken as limitative.

The illustrated amplifier comprises three stages respectively employing the pentode tube M of the variable-mu or gradual bias cut-off type, the similar pentode tube 52, and the two power output pentode tubes 33 in push-pull arrangement. The amplifier input terminals H are coupled to the grid of tube ll by the input transformer M (with secondary loaded if desired by resistance 55) and condenser 66; the tube d! is coupled to the grid of tube M by the coupling resistor 51 and the condenser 68; the tube a2 is coupled to the two tube 43 grids by the coupling resistor 49, the condenser 50, and the push-pull input auto-transformer 5i; and the two tubes 63 are coupled to the amplifier output terminals W by the pushpull output transformer 52. The grid return for the two tubes 33 may be connected to the negative terminal of a battery or other high-potential current source 53, and the cathodes of those tubes may be biased above the potential of that terminal through a bias resistor 54. The supply of screen and plate potentials to the several tubes, which may be from various points on the source 53, has been indicated simply schematically by arrows. .1

The cathodes of tubes M and 42 may be connected together, and biased to a potential slightly higher than that of the negative source terminal terminal of source 53.

respective tubes 4| and 42; and were these leaks returned simply to the negative sourceterminal, these tubes would always operate at full gain.

The leaks are returned (through filters 51, 58, I9-

hereinafter mentioned, and conductor 62) to that negative terminal, but this return also passes through a resistor Ell-across which the automatic volume control circuit, next described, at times builds up a voltage to render the tube 4| and 42 grids extra-negative, and thus to reduce their gain and thus that oi the amplifier.

The automatic volume control circuit may be simply provided by placing on the output transformer 52 a tertiary winding ii, in which voltage is developed in proportion to that across the output terminals, and connecting this in series with a rectifier'82 and the above mentioned resistor 60. The rectifier 62 is so poled that it passes current in the circuit 60-8 l-82 only in the direction of the arrow designated as We; this direction will be seen to be such that any resulting voltage drop in resistor 60 will always be poled to render conductor 63 more negative than the negative Thus it will be understood that when substantial output voltages appear across the output terminals II and hence across the tertiary winding 6|, pulsating unidirectional. current will fiow in the circuit 6li-6l--62, and a pulsating extra-negative potential (relative to the negative source terminal) will appear on the conductor 63. This potential is passed to the grid leaks of the tubes 4| and 42 through the resistance-condenser filter 59 (59a-59b); additionally as to tube 42, through the resistance-condenser filter 58 (Sid-58b); and additionally as to tube 4|, through the twostage resistance-condenser filter 51 (Ha-51b, and 510-5111). These filters substantially eliminate the pulsations from the extra-negative potential in question; and the net results are the applications to the grids of tubes 4| and 42 -of a substantially smooth extra-negative bias, and a reduction of their and the amplifier gain, of

degree responsive to the amplifier output voltage. By employment of a s'ufilciently large tertiary winding 6|, the amplitude of the extranegative bias may be made high enough so that for a very wide range of input voltage (across 11) the amplifier gain will vary almost inversely as that input voltage, and the output voltage (across ill) will vary only slightly. So the volume contrast-reduction or range-restriction is efiected. v I

It may here be mentioned that this contrastreduction or range-restriction may broadly be described as a modification (e. g., reduction) of the ratio of output to input energies of the common system portion (e. g., the amplifier).

It may be noted that the resistance-condenser filters 51, 58 and 59 must provide a suflicient attenuation of low as well as other frequency components to avoid self-oscillation of the amplifier through feed-back, and must at thesame time not be so unreasonably large in respect of individual series resistance and shunt capacity 7 as to result in undue time delay in the operation ofthe automatic volume control-the arrangement of the filters as a plurality of sections being I a convenient means to. the joint attainment of these ends.

I The connection from the rectifier 62 to the reed in neutral) sistor 80 has been shown as made through a small portion of the source 53-1. e., to a point P' of slight positive potential in that source. This is desirably done so that relatively'weak input and output voltage will .not cause the development of any extra-negative bias or any amplifier gain reduction-in other words, so that no volume control action is produced with very weak input voltages which, being for example'appreciably below theoptimum recording level, should at least be recorded with that full amplitude which they actually do possess. This result is secured because the inclusion of the small steady potential in the circuit SlI-fl-GZ, of polarity tending to render the cathode of the rectifier more positive than the anode, prevents any current fiowin that circuit until the. peak voltage from 6! has risen above a threshold value represented by the steady potential in question.

- To avoid the extra and useless distortion which would result from the use of the automatic volume control action in reproduction I provide means, responsive to a reproducing adjustment of the phonograph system, for eliminating that action. I have shown this means, more specifically, responsive to a reproducing position of lever l or rod 40; and still more specifically, to. a reproducing position oi switch 22. Most conveniently such responsiveness is secured by including in that switch an additional pole member 29 and an additional contact member 30, appropriately associated electrically with the automatic volume control circuit; In the case of the particular circuit 60-6l62 which has been illustrated, elimination of automatic volume control action is most conveniently secured by simple open-circuiting. So that circuit has been made serially to include the contacts or terminals I9, connected by leads 39 and 40 to the switch members 29 and 30 just above mentioned; and those switch members have been arranged to be closed against phonograph system is adjusted (as in Figure 1) for recordation, and to be out of contact with each other, opening the circuit, when. the system is adjusted (as in Flgure 2) for reproduction (and, if desired and as illustrated, when adjust- Itjgis course to be understood, however, that ,intended no ,limitation to the details I arrangement which has been shown, for, le ely providing and eliminating the volume contrast-reducing or range-compressing (e. g., automatic volume control) action, as such details will naturally be varied in accordance with the particular means employed for producing that action in any given case. 1

Figures 1 and 2 have contemplated theuse of separate recorder. and reproducer, and the use 01' separate microphone and loudspeaker (or its equivalent, an earphone or the like). The re- I each other, completing the circuit, when .the v corder and reproducer may, however, be combined into a single unit with or without distinct styli; or the loudspeaker and microphone may be combined into a single unit. Both such com-' iii viously then themselves be merged if'desired); and both of such mergings of leads have accordingly been illustrated in Figure 3.

While in Figures 1 and 2 I have shown the modification of 'automatic'volume control action, occurring upon change from recordation to reproduction, as arr infinite one (i. e. the reduction or that action to a zero value), my invention broadly embraces any modification of that action. So in Figure 3 I have schematically indicated the optional inclusion of a resistor 6d across the leads 39 and tit, and thus across the automatic volume control circuit contacts or terminals i9. This obviates full opening of the automatic volume control circuit during reproduction, and instead causes a finitely reduced volume control action then to obtain, in view of a division of rectified voltage between the active resistor 68 and'the passive resistor 5, in substantial proportion to their values.

It will of course be understood that while I have shown an arrangement whereby the automatic volume .control action is eliminated with the control lever 8 in neutral as well as in reproducing position, the matter of whether it is or is not eliminated in the neutral adjustment is ordinarily immaterial. It is further to be understood that while I have shown the switching means as manipulated immediately at the phonograph 9 (e. g., by lever 8), my disclosure is obviously likewise adapted for use with remote or remotely controlled switching. Further, I may call attention to the simplicity of the arrangement-21. single-pole, single-throw switch (Ed-30) across the serial contacts or terminals iii-for including or eliminating the automatic volume control action, which I believe to be of utility in itself, independently of association with the recording-reproducing switching means.

Finally itwill be understood that while I have disclosed my invention in terms of specific embodiments thereof, I do not intend that its scope be limited by the details of those embodiments;

rather I intend in the appended claims to set forth its scope as broadly as the state of the art will permit.

I claim:

1. In a phonograph system selectivey adapted for the recordation and reproduction of sound: the combination of a record support; recordcooperating translating means; selective control means for moving said translating means selectively into recording and reproducing relationships to a record on said support; means for effecting a compression of the volume range of 1 said sound; and means, controlled by said selective control means, for controlling said compression-eii'ecting means.

2. In a phonograph system selectively adapted for the recordation and reproduction of sound: the combination of a record support; recordcooperating translating means; selective control means for moving said translating means selectively into recording and reproducing relationships to a record on said support; means for effecting a reduction of volume contrasts in said sound; and means, controlled by said selective control means, for controlling said reductioneifecting means.

3. In a phonograph system selectively adapted for the recordation and reproduction of sound: the combination of a record support; record-cooperating translating means; selective control means, movable to recordation and reproduction positions, for moving said-translating means searcae'rr lectively into recording and reproducing relationships to a record on said support; means for eifecting a compression of the volume range of said sound; and means, rendered effective by said selective control means when in reproduction position, foreliminating said compression.

1 4. In a phonograph including a record support: the combination of record-cooperating translating means; selective control means for mov-.

5. In a phonograph including a record support:-

the combination of record-cooperating translating means; selective control means for moving said translating means selectively into recording and reproducing relationships to a record on said support; an electrical amplifier feeding said translating means during recordation and fed by said translating means during reproduction;

means associated with said amplifier for modifying the relationship between input and output energies thereto and therefrom; and means, controlled by said selective control means, for controlling said modifying means.

6. In a phonograph including a record support: the combination of record-cooperating translating means; selective control means, movable to recordation and reproduction positions, for moving said translating means selectively into recording and reproducing relationships to a record on said support; an electrical amplifier feeding said translating means during recordation and fed by said translating means during reproduction; automatic volume control means associated with said amplifier; and means, rendered effective by said selective control means when in reproduction position, for placing said automatic volume control means out of operation.

7. In a. phonograph system selectively adapted for the recordation and reproduction of sound: the combination of a record support; record-cooperating translating means movable selectively into recording and reproducing relationships to a record on said support; protective means, moved incidentally to the movement of said translating means, for preventing the removal of a record from said support; an electrical amplifier feeding said translating means during recordation and fed by said translating means during reproduction; volume compressing means associated with said amplifier; and means, associated with and responsive to the position of said protective means, for controlling said compressing means.

8. In a phonograph system for both sound recordation and sound reproduction, including a record support and record-coacting recording and reproducing means: selective means for adjusting said record-coacting means for sound recordation and sound reproduction; protective means responsive to said selective means for preventing the removal of a record from said support; an electrical amplifier; electro-acoustic translating means; and switch means, associated with and operated by said protective means, for variously associating said record-coacting means and said electro-acoustic translating means with said amplifier.

ORVILLE M. DUNNING. 

